1. Field of the Invention
The present invention relates to a process for the preparation of alkyl sulfate powders having a high bulk density.
2. Description of the Background
The alkali metal salts of monoalkyl half esters of sulfuric acid, called alkyl sulfates herein, contain an alkyl group of between 8 and 22 carbon atoms, and are of increasing interest as anaerobically degradable anionic surfactants.
Alkyl sulfates are obtained on an industrial scale by reacting alcohols with sulfur trioxide and then neutralizing the chemically labile half ester of sulfuric acid which is formed thereon using suitable aqueous bases, such as sodium hydroxide solution or aqueous sodium carbonate solution. The alkyl sulfates are produced as aqueous solutions, dispersions or pastes. These forms frequently make further processing difficult and are unsuitable for certain applications. For example, the presence of water, in particular, is found to be undesirable for many applications, requiring removal. Further, the additional weight of water adds considerable expense to the cost of transportation.
The removal of water, where required, can be effected in a variety of ways as long as the process used affords a solid which can be further processed with ease.
It is particularly advantageous to prepare alkyl sulphate powders from aqueous solutions since, in contrast to granules or flakes, for example, powders can be directly mixed with other powders to give final formulations and, in addition can be rapidly dissolved in water. In order to convert aqueous solutions of alkyl sulfates into powders, a plurality of processes are conceivable in principle. However, the process employed depends on both the physical and chemical properties of the alkyl sulfate solution to be dried and on the desired powder properties.
One such process is spray drying. For example, JP 54 10 6428 teaches such a process and that the alkyl sulfate slurries used must have a solids content of at least 60 to 80%, in order to be able to prepare powders having bulk densities above 200 g/l, which is, nevertheless, inadequate for further handling. Further, slurries having a surfactant content this high, according to the teaching of EP 0 084 154, can only be handled with equipment if particular measures are taken, such as the addition of additives of the same type. However, the substances which can be used for this purpose have certain disadvantages. They can, for example, impair the usability of the powders in a final formulation or, as a result of a low melting point, they can make the spraying, itself, difficult, since they promote clumping of the powders.
Thus, a need exists for alkyl sulfate powders having a high bulk density and which can be easily handled subsequent information.